Composite Columnar Structure Having Co-Bonded Reinforcement and Fabrication Method

ABSTRACT

A columnar structure comprises a generally hollow laminate core, an outer composite skin, and a sleeve-like reinforcement. The sleeve-like reinforcement surrounds the laminate core and is sandwiched between the laminate core and the outer composite skin for reacting compressive loads imposed on the columnar structure.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to co-pending U.S. patent application Ser. No. 13/288,491 filed Nov. 3, 2011, which is incorporated by reference herein in its entirety.

BACKGROUND INFORMATION

1. Field

The present disclosure generally relates to composite columnar structures, and deals more particularly with a hybrid composite tubular strut internally reinforced to better resist axial compression loads.

2. Background

Columnar structures formed of composites are used in a variety of applications because of their favorable strength-to-weight ratio. For example, composite tubular struts may be used in the aerospace industry as a support or brace for transferring loads in either direction along the longitudinal axis of the strut, thus placing the strut in either compression or tension. Fittings on the ends of the strut provide additional strength at the points of attachment of the strut to a structure.

The tubular struts mentioned above may be fabricated from fiber reinforced resin laminates. Such laminates may exhibit greater load carrying ability when placed in tension than when placed in compression. This is because the compressive strength of the resin is generally less than its tensile strength. Consequently, in order to meet performance specifications, it may be necessary to over-size the strut to carry a specified level of compression loading. Over-sizing the strut, however, may add cost and/or undesired weight to a vehicle or other structure to which the strut is attached.

Accordingly, there is a need for a composite columnar structure that exhibits improved ability to carry compression loads. There is also a need for a cost effective method of making a columnar structure with improved compression load carrying ability that adds little or no weight to the structure.

SUMMARY

The disclosed embodiments provide a composite columnar structure such as a tubular strut that exhibits an improved ability to resist axial compression loads while adding little or no weight to the structure. Improved compression load capability is achieved by incorporating a sleeve-like reinforcement around laminated plies forming a core of the strut. The reinforcement allows composite tubular struts and similar columnar structures to be designed that are “right-sized” to meet both compression and tension load carrying specifications while minimizing the weight of the strut.

According to one disclosed embodiment, a columnar structure is provided comprising a generally hollow laminate core, an outer composite skin, and reinforcement. The reinforcement surrounds the laminate core and is sandwiched between the laminate core and the outer skin for reacting compressive loads imposed on the columnar structure. The laminate core may be substantially tubular and the reinforcement may include a layer of material extending substantially completely around the laminate core. The layer of material may be one of a metal such as without limitation, titanium, a precured fiber reinforced composite or a ceramic, and the laminate core may be a fiber reinforced resin such as a carbon fiber reinforced plastic. The reinforcement may comprise first and second halves that are seamed together in a direction parallel to the axis of the laminate core. In one embodiment, the reinforcement may include corrugations on the inside wall thereof which may control wrinkling of underlying laminate plies of the core during consolidation and curing of the laminate.

According to another embodiment, a strut comprises a generally tubular, fiber reinforced resin core, and a sleeve-like reinforcement around the core having a compressive strength greater that the compressive strength of the resin. The sleeve-like reinforcement may be a corrugated metal, and may include first and second halves assembled together along seams extending in the longitudinal direction of the tubular core. The strut may further comprise a pair of spaced apart end fittings including a pair of attachment pins adapted to attach the strut to a structure. The pins lie substantially in a first plane, and the seams lie substantially in a second plane generally perpendicular to the first plane. In one variation, the sleeve-like reinforcement is a ceramic. In another variation, the sleeve-like reinforcement is titanium, and the fiber reinforced resin core is carbon fiber reinforced plastic. The sleeve-like reinforcement is co-bonded to the core and to the outer skin.

According to still another embodiment, a method is provided of making a strut, comprising fabricating a composite laminate core, fabricating a sleeve-like reinforcement, assembling the reinforcement over the core, and fabricating an outer skin over the sleeve-like reinforcement. The method may further comprise co-bonding the sleeve-like reinforcement to the core and to the outer skin. Fabricating the sleeve-like reinforcement may include forming corrugations on an inside face of a metal member. Fabricating the composite laminate core includes laying up plies of a fiber reinforced resin, and assembling the sleeve-like reinforcement over the core includes placing the metal member on the core with the corrugations against the laid up plies of the core. The method may further comprise consolidating and curing the core, and using the corrugations on the metal member to control wrinkling of the plies during the consolidation.

The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and descriptions thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is an illustration of a perspective view of a hybrid composite tubular strut exhibiting an improved ability to resist axial compression loads according to one disclosed embodiment.

FIG. 2 is an illustration of a sectional view taken along the line 2-2 in FIG. 1.

FIG. 3 is an illustration of a perspective view of the strut shown in FIG. 1 in an intermediate stage of fabrication in which two halves of a reinforcement are being installed on a laminate core.

FIG. 4 is an illustration similar to FIG. 3, but showing the two halves of the reinforcement having been installed.

FIG. 5 is an illustration similar to FIG. 4 but showing an alternate embodiment of the reinforcement having corrugations.

FIG. 6 is an illustration of a perspective view of the corrugated reinforcement, in the area shown as 6-6 in FIG. 5.

FIG. 7 is an illustration of the area designated as FIG. 7 in FIG. 2, but illustrating use of the corrugated form of the reinforcement.

FIG. 8 is an illustration of a cross sectional view of another form of the reinforcement.

FIG. 9 is an illustration of a flow diagram of a method of fabricating a hybrid composite columnar structure according to the disclosed embodiments.

FIG. 10 is an illustration of a flow diagram of aircraft production and service methodology.

FIG. 11 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIG. 1, a composite columnar structure illustrated as an elongate strut 20 includes a generally cylindrical, tubular body 22 and a pair of end fittings 24 for attaching the strut 20 to a structure (not shown). The strut 20 may function to transfer compression loads along the longitudinal axis 25 of the tubular body 22, and may also transfer loads that place the tubular body 22 in tension. Each of the end fittings 24 may be made of a metal such as aluminum or titanium, or a composite or other suitable materials. The end fittings 24 may be fabricated by casting, machining, or other common manufacturing techniques. In applications where the end fittings 24 are formed of composite materials, they may include metallic inserts and/or metallic bushings (not shown).

Each of the end fittings 24 may include a clevis 26 having a central opening 28 aligned along an axis 32 for receiving a clevis pin 30 that attaches the strut 20 to the structure. The axes 32 of the clevis pins 30 lie substantially in the same plane 35. The clevis pins 30 along with clevis 26, form pivotal connections between the strut 20 and the structure to which it is attached. The strut 20 may be employed, for example and without limitation, as a brace between an aircraft engine (not shown) and an airframe (not shown). Any of a variety of other types of end fittings 24 are possible, depending on the intended use of the strut 20. Also, as previously mentioned, the strut 20 may function to transfer axial loads biaxially along the longitudinal axis 25 of the strut 20 so that the strut 20 may be placed either in tension or compression or both in an alternating fashion along the longitudinal axis 25. In some applications, the strut 20 may also experience limited torsional loading. In the illustrated example, the cross sectional shape of the tubular body 22 is substantially round and constant along its length, however other cross sectional shapes are possible, such as, without limitation, square, triangular, hexagonal or pentagonal shapes. Also, the tubular body 22 may have one or more tapers along its length.

Referring now to FIG. 2, the tubular body 22 broadly comprises a generally cylindrical, sleeve-like reinforcement 36 sandwiched between a cylindrical core 34 and an outer skin 38. The sleeve-like reinforcement 36 increases the compressive strength of the tubular body 22. The core 34 may comprise multiple plies 48 (FIG. 7) of a suitable fiber reinforced resin, such as, without limitation, carbon fiber reinforced plastic (CFRP) that may be laid up over a removable mandrel (not shown) by manual or conventional automated layup techniques. The outer skin forms a protective covering over the sleeve-like reinforcement 36 and may also comprise multiple laminated plies of a fiber reinforced resin. The plies of the outer skin 38 also hold the sleeve-like reinforcement 36 in place and may enable the reinforcement 36 to better resist compressive loading.

In one embodiment, the sleeve-like reinforcement is cylindrical in shape and may comprise a layer of material 42 formed as semi-circular first and second reinforcement halves 36 a, 36 b that extend substantially the entire length of the tubular body 22. In other embodiments, the layer of material 42 may comprise a single member or more than two members. The layer 42 may comprise a suitable material that exhibits the desired degree of compression strength, such as a metal foil or a ceramic, and is compatible with the material forming the core 34. For example, where the core 34 is formed of CFRP, the layer of material 42 forming the reinforcement 36 may comprise titanium. The layer 42 may also comprise a precured resin that contains unidirectional reinforcement fibers such as, without limitation, steel fibers which resist axial compression loads applied to the strut 20. The compressive strength of the sleeve-like reinforcement 36 is greater than that of the resin forming the core 34 in order to increase the overall compressive strength of the strut 20.

In the illustrated example employing a two-piece reinforcement 36, the halves 36 a, 36 b may be preformed and then assembled around the core 34, forming diametrically opposite joint lines or seams 44. The reinforcement halves 36 a, 36 b may or may not be mechanically joined along the seams 44. In one embodiment, although not shown in the Figures, the two halves 36 a, 36 b may overlap each other along the seams 44 in order to allow the halves 36 a, 36 b to slip relative to each other and collapse slightly as the underlying core 34 shrinks during consolidation and curing of the core 34. The thickness “T” of the layer of material 42 may vary with the application, depending upon the amount of compressive strength that is desired to be added to the strut 20. While only a single cylindrical reinforcement 36 is shown in the illustrated example, the strut 20 may include multiple axially concentric reinforcements 36 (not shown) embedded in the tubular body 22. In still other embodiments, the reinforcement 36 and/or the core 34 may taper from a thin cross section portion to a thicker cross section portion along the length of the tubular body 22, while the outer cylindrical shape of the tubular body 22 remains substantially constant.

Referring to FIG. 3, strut 20 may be assembled by laying up plies 48 (FIG. 7) of the core 34 over end fittings 24, however other methods of attaching the end fittings 24 to the core 34 are possible. The two halves 35 a, 36 b of the sleeve-like reinforcement 36 may be preformed by any suitable process, and then assembled over the core 34. Depending of the thickness “T” (FIG. 2) of the reinforcement 36, the reinforcement 36 may be formed-to-shape by forming a layer of material 42 over the core 34, using the core 34 as a mandrel. FIG. 4 illustrates the two halves 36 a, 36 b having been assembled over the core 34 and depicts one of the seams 44, which, as previously mentioned, may represent a mechanical joint line attachment of the two halves 36 a, 36 b. The circumferential location of the seams 44 may be chosen so as to optimize the buckling strength of the tubular body 22. For example, in the illustrated embodiment, the seams 44 may be located circumferentially such that they lie in or near a plane 37 (FIGS. 1 and 2) that is substantially perpendicular to the plane 35 of the clevis pins 30. Orienting the seams 44 generally perpendicular to the axes of the pins 30 in this manner may better enable the reinforcement 36 to resist bending moments in a plane near or substantially parallel to or within the plane 35 and thereby improve the bucking strength of the strut 20. However, it should be noted that the benefits provided by the disclosed embodiments may be realized even when the seams 44 are not located at circumferential positions that optimize the buckling strength of the strut 20.

FIG. 5 illustrates an alternate embodiment of the strut 20 that includes a two-piece sleeve-like cylindrical reinforcement 36 having corrugations 46. Referring to FIG. 6, the corrugations 46 include circumferentially spaced, longitudinally extending corrugation ridges 46 a on the inside face 45 of the reinforcement 36. The corrugations 46 may be formed by any of a variety of processes that are suited to the material from which the reinforcement 36 is made. Referring to FIG. 7, it can be seen that the ridges 46 a of the corrugation 46 extend down into and are compressed against the laminated plies 48 of the core 34. During consolidation and curing of the strut 20, the core shrinks and the corrugation ridges 46 a are compacted against the core 34, tending to control wrinkle formation in the plies 48 of the core 30. This wrinkle control is achieved as a result of the corrugation ridges 46 a depressing and lengthening portions of the plies 48 around the ridges 46 a in order to tighten and/or absorb the shrinkage of the plies 48 during consolidation/curing.

The ability of the sleeve-like reinforcement 36 to control wrinkling of the underlying plies 48 during the consolidation process may be achieved using other forms of the reinforcement 36. For example, referring to FIG. 8, in lieu of corrugating the layer of material 42 comprising the reinforcement 36 as described above, longitudinally extending, spaced apart raised strips 47 of any suitable material may be applied by a suitable technique to the inside face 45 of the layer of material 42, either before or after the layer of material 42 has been formed into the desired shape.

Attention is now directed to FIG. 9 which illustrates the overall steps of a method of fabricating the composite tubular strut 20 described previously. Beginning at 50, laminated core 30 is fabricated by laying up composite plies 48 over a suitable mandrel (not shown), which may be for example, an inflatable or ablative mandrel. Next, at 52, the reinforcement 36 may be fabricated either by preforming one or more layers of material 42 into halves 36 a, 36 b of the desire cross sectional shape, or by forming the material over the core 30, using the core 30 as a mandrel. At step 54, a suitable adhesive is applied over the core 30, following which at 56, the reinforcement 36 is assembled over the core 30. The seams 44 between the reinforcement halves 36 a, 36 b may be located such that they lie substantially in a plane 37 that is substantially perpendicular to the plane 35 of the clevis pin 30 axes 32 in order to better resist bending forces, however, the seams 44 may be located at other points, depending on the construction and geometry of the end fittings 24. At step 58 a suitable adhesive is applied over the reinforcement 36. At step 60, outer skin is applied over the reinforcement 36 by laying up additional composite plies over the reinforcement 36. At step 62, the strut 20 is debulked, compacted and cured, thereby co-bonding the reinforcement 36 to the core 30 and the outer skin 38. Finally, at step 64, the mandrel on which the core 30 is laid up may be removed.

Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where automated layup equipment may be used. Thus, referring now to FIGS. 10 and 11, embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method 70 as shown in FIG. 10 and an aircraft 72 as shown in FIG. 11. Aircraft applications of the disclosed embodiments may include, for example, without limitation, load transferring members such as struts, supports, connecting rods and similar columnar structures. During pre-production, exemplary method 70 may include specification and design 74 of the aircraft 72 and material procurement 76. During production, component and subassembly manufacturing 78 and system integration 80 of the aircraft 72 takes place. Thereafter, the aircraft 72 may go through certification and delivery 82 in order to be placed in service 84. While in service by a customer, the aircraft 72 is scheduled for routine maintenance and service 86, which may also include modification, reconfiguration, refurbishment, and so on.

Each of the processes of method 70 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.

As shown in FIG. 11, the aircraft 72 produced by exemplary method 70 may include an airframe 88 with a plurality of systems 90 and an interior 92. Examples of high-level systems 90 include one or more of a propulsion system 94, an electrical system 96, a hydraulic system 98, and an environmental system 100. Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries.

Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method 70. For example, components or subassemblies corresponding to production process 78 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 72 is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages 78 and 80, for example, by substantially expediting assembly of or reducing the cost of an aircraft 72. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft 72 is in service, for example and without limitation, to maintenance and service 86.

The description of the different advantageous embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated. 

1. A columnar structure, comprising: a generally hollow composite laminate core; an outer composite skin; and a reinforcement surrounding the composite laminate core and sandwiched between the composite laminate core and the outer composite skin for reacting at least compressive loads imposed on the columnar structure.
 2. The columnar structure of claim 1, wherein: the composite laminate core is substantially tubular, and the reinforcement includes a sleeve-like layer of material extending substantially completely around the laminate core.
 3. The columnar structure of claim 2, wherein: the sleeve-like layer of material is one of a metal and a ceramic, and the composite laminate core is a fiber reinforced resin.
 4. The columnar structure of claim 2, wherein: the sleeve-like layer of material is titanium, and the composite laminate core is a carbon fiber reinforced plastic.
 5. The columnar structure of claim 1, wherein the reinforcement is a metal having first and second halves seamed substantially along a longitudinal axis of the composite laminate core.
 6. The columnar structure of claim 1, wherein the reinforcement includes a sleeve-like layer of material having corrugations in contact with the composite laminate core and extending in a longitudinal direction of the composite laminate core.
 7. A strut, comprising: a generally tubular, fiber reinforced resin core; and a sleeve-like reinforcement around the fiber reinforced resin core having a compressive strength greater than the compressive strength of the fiber reinforced resin core.
 8. The strut of claim 7, wherein the sleeve-like reinforcement is a metal.
 9. The strut of claim 7, wherein the sleeve-like reinforcement is corrugated.
 10. The strut of claim 8, wherein the sleeve-like reinforcement includes first and second halves assembled together along seams extending in a longitudinal direction of the fiber reinforced resin core.
 11. The strut of claim 10, wherein the seams are located at positions around the fiber reinforced resin core that substantially optimize the buckling strength of the strut.
 12. The strut of claim 10, further comprising: a pair of spaced apart end fittings including a pair of attachment pins lying substantially in a first plane and adapted to attach the strut to a structure, and wherein at least one of the seams lies substantially in a second plane generally perpendicular to the first plane.
 13. The strut of claim 7, wherein the sleeve-like reinforcement is a ceramic.
 14. The strut of claim 7, wherein: the sleeve-like reinforcement is titanium and has an inside face with longitudinal raised strips thereon, and the fiber reinforced resin core is carbon fiber reinforced plastic.
 15. The strut of claim 7, wherein the sleeve-like reinforcement includes first and second halves each having an inside face provided with ridges in contact with the fiber reinforced resin core.
 16. The strut of claim 15, further comprising: an outer skin covering the sleeve-like reinforcement, wherein the sleeve-like reinforcement is co-bonded to the fiber reinforced resin core and to the outer skin.
 17. A method of making a strut, comprising: fabricating a composite laminate core; fabricating a sleeve-like reinforcement; assembling the sleeve-like reinforcement over the composite laminate core; and fabricating an outer skin over the sleeve-like reinforcement.
 18. The method of claim 17, further comprising: co-bonding the sleeve-like reinforcement to the composite laminate core and to the outer skin.
 19. The method of claim 17, wherein: fabricating the sleeve-like reinforcement includes forming corrugations on an inside face of a member, fabricating the composite laminate core includes laying up plies of a fiber reinforced resin, and assembling the sleeve-like reinforcement over the composite laminate core includes placing the member on the composite laminate core with the corrugations against the plies of the composite laminate core.
 20. The method of claim 19, further comprising: consolidating and curing the composite laminate core, and using the corrugations on the member to control wrinkling of the plies during the consolidation.
 21. The method of claim 20, wherein the plies are laid up on a mandrel, and further comprising removing the composite laminate core after curing and consolidation are performed.
 22. The method of claim 17, wherein fabricating the sleeve-like reinforcement includes fabricating first and second halves.
 23. The method of claim 22, wherein assembling the sleeve-like reinforcement over the composite laminate core includes placing the first and second halves over the composite laminate core and arranging seams between the first and second halves in a longitudinal direction of the composite laminate core.
 24. The method of claim 17, further comprising: using the sleeve-like reinforcement to control wrinkling of the composite laminate core during consolidation and curing of the composite laminate core. 